Diversity receiving system



Nov. 2, 1943. H. o. PETERSON DIVERSITY RECEIVING SYSTEM Filed Aug. 12, 1941 I T T .www E 0 PETERSN (WWl/ INVENTOR ATIORNEY HAROL Erw URNQIN mu Nv &

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mw E* y 2 Patented Nov. 2, 1943 UNITED DIVERSITY RECEIVING SYSTEM Harold 0. Peterson, Riverhead, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application August 12, 1941, Serial No. 406,471

(Cl. Z50- 20) 12 Claims.

This invention relates to diversity receiving systems and more particularly to that type of a diversity system in which means are provided for automatically switching the signals through alternative amplifiers at the receiving station so as to maintain connection of a responsive device with the path over which the signal of greatest amplitude is arriving at any particular moment.

In the usual diversity receiving system, the same transmitted signal is simultaneously receiVed on different antennae. The amplitude of the received signals at different antennae is quite frequently varied because of multipaths over which the signals are communicated through Space. The signals received over paths of different length are apt to be combined at any one antenna in an out-of-phase relation. At such times, the signal must be utilized as received at an antenna where an in-phase relation exists.

My invention is particularly adapted for use in radio communication systems employing amplitude modulation, phase modulation or single side band transmission. In accordance with any'of these methods, it may be of advantage to use an exalted carrier in the local receiver.

It is an object of my invention to provide a diversity receiving system which is suitable for use in association withradio receiving apparatus that may be responsive to either frequency modulated signals, phase modulated signals, amplitude modulated signals or a single side band communication system.

It is another object of my invention to provide a form of diversity receiving system whereinthe carrier wave is exalted and where use is made of a signal energy component from a narrow band filter for switching into service one of a plurality of amplifiers, each connected in a different receiving channel. e

It is another object of my vinvention to provide a diversity receiving system in which reception is improved by the use vof carrier wave filters and modulation band filters bothfeeding in to balanced detectors, the output `from which may be utilized in a system of alternative amplifiers which vare selected for feeding the signal energy into a responsive device in dependence upon the energy control derived from the particular' receiving channel uponwhich the strongest signal is impressed.

Other objects of my invention will be made apparent in the description to follow.

My invention will now be described` in4 more detail, reference being made to the accompanying drawing, the sole gure of which shows diagrammatically a circuit arrangement of a preferred embodiment.

Referring to the drawing, I show two antennae I and 2 which are presumed to be geographically separated so as to receive signals conducted through space over different paths. The signals received on antenna I are fed to the radio frequency amplifier and converter 3 while signals from antenna 2 are likewise fed to a radio frequency amplifier and converter 4. These two units 3 and 4 are supplied with local oscillations from generator 5 for purposes of heterodyning.

Output currents from the converter units 3 and 4 are fed to intermediate frequency amplifiers and converters represented by the units 'I and 8 respectively. The unit 'I is served by a local oscillator 9 for purposes of producing a second intermediate frequency while the unit 8 is likewise served by a local oscillator I0 for producing a corresponding second intermediate frequency with respect to the signals received on antenna 2. If desired, the signals fed to units 1 and 8 may be heterodyned with oscillations from a single generator replacing the units 9 and IB.

The output from the converter unit 'l is fed to two sepa rate filters II and I3, and similarly the output from the converter unit 8 is fed to two separate filters I2 and I4. The filters II and I2 are designed to pass a very narrow band of frequencies such as the carrier frequency plus and minus a few cycles. The filters I3 and I4, however, are characterized as having a pass band sufciently wide to cover the entire modulation range.

Since the filters II and I2, normally pass only the carrier frequency, or, as an alternative some pilot tone frequency, I preferably utilize the output therefrom to operate a switching means and automatic gain control circuit presently to be described. The outputs from filter units Il and I3 are, however, combined in a balanced detector comprising discharge tubes 4I and 43, and the combined energy is fed therefrom to a so-called alternative amplifier I1. Correspondingly, the outputs from the filter units I2 and I4 are combined and rectified inthe balanced detector comprising discharge tubes 42 and 44, and fed therefrom to the alternative amplifier I8.

The balanced detector tubes 4I and 43 are controlled by energies derived from the secondaries of transformers 35 and 31. One terminal of the secondary of transformer 35 is connected through a biasing source 39 to the grounded cathodes of tubes 4I and 43, wliilethe other terminal of this transformer secondary is connected to a mid-tap on the secondary of transformer 31. The terminals of the last mentioned secondary are connected respectively to the grids of the tubes 4I and 43. Output from the modulation band illter I3 is fed directly to the primary of transformer 31. Output from the carrier frequency lter II is fed through a phase adjuster 33 to the primary of transformer 35.' The anodes of tubes 4I' and 4'3 are connectedto the two terminals of the primary Winding on transformer 41, the secondary of which is in the input cir'- cuit for the amplifier I1. 4I and 43 are connected through an anode potential source 45 to a mid-tap on the primary-ot. transformer 41. i

The circuit arrangement shown for the balanced detector tubes 42 and 44 inthe other. of the diversity receiving channels is identically like that already described. In other words, .theev'en numbered phase adjuster 34,. the three transformers 3S, 3U and 48', the biasing source Jil and the anode potential source 46 correspond with like parts which bear odd numbersin thel circuit already described'.

The phase adjust-'ers 33` and 34 are required for obtaining proper detection, depending. upon Whether the system is to be used forrecepti'cn of phase modulated signals, or amplitude modulated signals. In changing from phase modulation to amplitudemodulation, the phase adjusters wouldbe. sliifted'QOc". Itis obvious, however, that the balanced detector may also serve for single' side-band. reception..

The output circuits from the amplifiers IT and. I8 are combined'y andv connected` to any suitable utilization device. These amplifiers are" so con'- trolledby two diode recti'flers IS. and' 2U respectively` thatusually onlyone' of them isv rendered operative at any' onetime. This isaccomplished by the use" of a D.' C. biasing potential ou the' control grids ofi the amplifier tubes such that they can amplify inputA energy only inl the presence.

of a rectrfledsignai component from one; or the* other of the rectm'ers I's' and 25. Rectifier IS` receives signal energy through the secondary" of transformer 2i, they primary of which is con- `rrected in' an output circuit from' the narrow band filter unit' IL Likewise, rectifier 20 is fed with signal' energy fromV the' secondary of transformer" 22;,the primary of which isk fed with signal energy derived' from( the' narrow` band filter` l2 The rectied signal:` energy is impressed across rcsrstcrs 2'3 and' 24 depending uponl the respective amplitudes of" the signals received on the' two antennae I and 2. The stronger the signal the more positive will he the cathcdes o! the tubes f'Q-'and 2U. The positive potentialv thus obtained operates' to'unbloclc the amplifiers' if and Il.

'The` rectiers t9 and 211v a common load,

impedance 25.'- Thc potentials-X developed4 across thisln'ipeda-ncefl5I are fed' through arifimpedaucej 29' thence-toithe various units 3, 4, 1' and' K forV controlling the gain therein. Capacitor 30', one' side of whichIv isf grounded and. the. other' sidel of iisvcmmected to the automatic gain. contrui cn'cnit, @operates with: the' imizve'darxce` 29 for contronug theftmse constant'of the automatic gain: confermi.y circuit. Capacitors: 21 and 20 are disposed betweentliesrcspcctive cathodes of rectmers I9 and 20; and ground? in. order to by- :s1-terriating` current components` of the` recttmadonergy.. Capacitor 26de also am alternating. currently-pass to ground.

loris preferable' to auto*tritati@rallyv control the tramway.' of the locas oscillators 9 and |50, and

The cathodes of tubes for this purpose automatic frequency control devices 3| and 32 are employed. These devices are controlled by output energy from the narrow band filters II and I2.

If the load impedance 25 is made large compared with the imped'ances 23 and 24, it is found that diode current will flow only in that rectifier having the strongest impressed signal voltage. Consequently, the control voltage required for switching thev alternatrw: amplifiers I'F and I8 in and out of service is, in general, such that only one of these ampliers will be operative at any signals through an appropriate alternative amplilierr to a. common utilization device. the method of improving; reception which comprises separating out from a modulationv frequency a nar: row: frequency band including: the signal' car- 30, ri'er, normally` blocking said: alternative ampliers with. respect to Weak signalsV fed' thereto from certain of said antennae, and'unbiocking: said alternative ampilners one. aty a time; each in. response to the carne:-- energy component de- 35 rived' from a. particular oney of said' antennae and fed to its appropriate grouper responsive devices, and duringa period whentl'ie amplitude or' saidlv componentin that group predominates" such. components in other; groups.

4@ 2; The method" according? to claim Iv and inoiudng the step of automatically controlling the gain insaid responsive devices' in' accordance with the amplitude of' the' Dredom'inating groupv derivative of said carrier energy.

3. In a diversity receiving; system Comprlshig a4 plurality of" radio reception branches comprisingv mpiiners connected to a common utilization device, a heterodme converterV in'. each brauch,` a modulation. `band filter and a narrowly selecti've carrier frequency lter in each branch., said filters' being coupled in parallel to the output circuit oftheir converted. a .phase adjuster in the output circuit of each carrier frequency lterr a, detectorin each branch under joint controly ofi modulated signals derived' from' said modulation band. l'ter and' of, carrier vwave energy fed through phase addusten, andV meansv controlled solely by rectled components of the filtered carrier energies in. the. respective branches for transferring to said utillza'tiondevl the products. of that one of said balanced detectors which is ofthe branchrecelving at the momont the strongest carrier wave..

4, A system in accordance with claim 3 andi including automatic gain control devices common to, and operable upon, the ampliers of said radio reception branches ln accordance with the strongest ot the carrier wave components. of thev several branches.v

5. A system in accordance with claim y3 in which said phase adiusters includev meansy settable to produce a conductance phase in said balanced detectors andr` in said utilization device' whereby. phase-modulated signals are translated mtolntelllgencet- 6. A system in accordance with claim 3 in which said phase adjusters include means settable to produce a conductance phase in said balanced detectors and in said utilization device whereby amplitude-modulated signals are translated into intelligence.

7. A diversity receiving system comprising a plurality of antennae, a separate radio frequency amplifying and heterodyning unit connected to each antenna, a pair of parallel connected filters for passing the output from each of said units, one lter in each pair having a modulation band pass characteristic, the other filter of each pair having a pass characteristic which is sharply selective of a given carrier wave, balanced demodulators each fed with suitably phaserelated energies derived from an appropriate pair of said filters, a plurality of normally blocked amplifiers each connected to receive the rectified output energy from an appropriate balanced demodulator, said amplifiers having a common output circuit feeding to a utilization device, and means for comparing the amplitudes of the output components from the respective sharply selective filters, said means being effective to unblock said amplifiers one at a time and each during a period in which the carrier component of the signal applied thereto is relatively the strongest.

8. A system in accordance with claim 7 wherein the last said means comprises a plurality of diode rectifier-s each having a cathode in circuit with a grounded cathode resistor, the several anodes of said rectifiers being in circuit with a common load resistor, the impedances of said cathode resistors being individually high with respect to the impedance of said common load resistor.

9. A diversity receiving system comprising a plurality of radio reception branches each fed with energy collected by a different antenna, filter means coupled to each branch for passing a narrow frequency band including the carrier wave, an amplifier for modulated frequency com.- ponents of the energy in each branch, each said amplifier being normally blocked With respect to relatively Weak signals, meansfor rectifying an output component from each said filter means, means including a system of impedances connected to each of said rectifying means whereby rectied current is derived solely from the branch having the strongest impressed signal voltage, and means responsive to the rectified current so derived for unblocking a particular amplifier, thereby to utilize only the modulated frequency signal components from the branch in which the carrier wave is strongest.

10. In combination, a pair of diode rectifiers each having an anode and a cathode, a first impedance carrying currents to be rectified and being connected between the anodes of said diodes, a second impedance interconnecting their cathodes, a third impedance interconnecting midtaps on the first and second impedances, respectively, a gain control circuit utilizing the voltage drop across the third impedance, and selective means differentially responsive to a voltage drop` in one arm of the second impedance when it exceeds the voltage drop in the other arm thereof.

11. In combination, a pair of diode rectifiers each having an anode and a cathode, a divided inductance carrying currents to be rectified and being connected across the anodes, a divided resistor interconnecting the cathodes, a capacitively-shunted resistor interconnecting the midpoints of said inductance and said divided resistor, means utilizing the potential drop across said capacitively shunted resistor, and other means f differentially responsive to the predominance of voltage drop in one arm as compared with the other arm of said divided resistor.

12. A circuit arrangement comprising a balanced detector having two diode discharge tubes,

two independent alternating current circuits each arranged to deliver an output component to a respective one of said tubes, whereby said component is rectified, an automatic gain control device common to the two translating circuits and operable by rectified output energy from said diode tubes, and switching means for connecting a selected one of said translating circuits to a common utilization device, said means being automatically controlled by the moment-to-moment predominance of rectied output energy derived from one over the other of said diode tubes.

HAROLD O. PETERSON. 

